The ANAIS-112 experiment at the Canfranc Underground Laboratory

Abstract

The ANAIS experiment aims at the confirmation of the DAMA/LIBRA signal at the Canfranc Underground Laboratory (LSC). Several 12.5 kg NaI(Tl) modules produced by Alpha Spectra Inc. have been operated there during the last years in various set-ups; an outstanding light collection at the level of 15 photoelectrons per keV, which allows triggering at 1 keV of visible energy, has been measured for all of them and a complete characterization of their background has been achieved. In the first months of 2017, the full ANAIS-112 set-up consisting of nine Alpha Spectra detectors with a total mass of 112.5 kg was commissioned at LSC and the first dark matter run started in August, 2017. Here, the latest results on the detectors performance and measured background from the commissioning run will be presented and the sensitivity prospects of the ANAIS-112 experiment will be discussed.

ANAIS-112 sensitivity in the search for dark matter annual modulation

“…We consider the spin-independent WIMP interaction, using the Helm nuclear form factor [30] and Q Na = 0.30 and Q I = 0.09 for the sodium and iodine quenching factors to transform the nuclear recoil energy into electron equivalent one, respectively [21]. The resolution of ANAIS-112 is estimated in [1,6] keV ee as Γ = 0.890 E(keV ee ) − 0.188, where Γ is the full width at half maximum [2]. The Earth velocity [31] is given by v E (t) = 232 + 15 · cos 2π · t − 152.5 365.25 km/s,…”

“…The ANAIS experiment [1,2] is intended to search for dark matter annual modulation with ultrapure NaI(Tl) scintillators at the Canfranc Underground Laboratory (LSC) in Spain, in order to provide a model independent confirmation of the signal reported by the DAMA/LIBRA collaboration [3][4][5] using the same target and technique. Projects like DM-Ice [6], COSINE-100 [7,8], SABRE [9] and PICO-LON [10] also envisage the use of large masses of NaI(Tl) for dark matter searches.…”

“…Nevertheless, DAMA/LIBRA has accumulated up to now twenty annual cycles in the [2,6] keV ee energy region (keV ee for keV electron-equivalent) with 12.8σ statistical significance (phase and period fixed) [3][4][5]. Moreover, DAMA/LIBRA-phase2 has been able to accumulate six annual cycles in the [1,6] keV ee energy region with 9.5σ statistical significance because all the photomultipliers (PMTs) were replaced by a second generation PMTs Hamamatsu R6233MOD, with higher quantum efficiency and with lower background with respect to those used in phase1 [5].…”

“…The time-averaged differential rate is denoted by S 0 , whereas the modulation amplitude is given by S m [21]. The value of S m measured by DAMA/LIBRA is 0.0102 ± 0.0008 and 0.0105 ± 0.0011 cpd/kg/keV ee within [2,6] and [1,6] keV ee intervals, respectively (cpd stands for counts per day) [5].…”

“…In this paper, we analyze the ANAIS-112 prospects in terms of the a priori critical and detection limits of the experiment and a simple figure of merit has been obtained to compare the different experiments looking for the annual modulation observed by DAMA/LIBRA. The structure of the paper is as follows: section 2 describes the ANAIS-112 experimental layout; section 3 focuses on the procedure to search for a modulation signal in the [2,6] keV ee energy region, considering a single energy bin and afterwards the energy binning and segmented detector in nine modules; section 4 focuses on the [1,6] keV ee energy region in view of the last DAMA/LIBRA-phase2 results. Finally, conclusions are presented in section 5.…”